Semiconductor memory device and manufacturing method thereof

ABSTRACT

The present invention is a high quality semiconductor memory device using a ferroelectric thin film capacitor as a memory capacitor at a high manufacturing yield, the ferroelectric thin film of the capacitor is specified such that the relative standard deviation of crystal grain sizes is 13% or less, to thereby ensure a high remanent polarization value and a small film fatigue (large rewritable number).

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor memory device using aferroelectric thin film, which is most suitable for a ferroelectricnonvolatile memory or high density DRAM, and to a method ofmanufacturing the semiconductor memory device.

(1) A conventional ferroelectric thin film capacitor has, as describedin “Ferroelectric Thin Film Memory” (published by Science Forum, 1995),page 227, a stacked structure of Pt upper electrode/ferroelectric layer(PZT)/Pt lower electrode.

(2) Based on a surface observation photograph by a scanning electronmicroscope for a PZT ferroelectric thin film crystallized on a lowerelectrode, described in Integrated Ferroelectrics, 1995, Vol. 10, pp.145-154, an average crystal grain size is about 180 nm and a relativestandard deviation of crystal grain sizes is about 15%.

(3) In a method of forming a thin film described in Japanese PatentLaid-open No. Hei 7-142600, a compound of BaTiO₃ is formed on a Pt thinfilm, whereby orientation of a ferroelectric thin film is controlled byallowing crystal orientation of the ferroelectric thin film to followthat of the Pt thin film, to thereby ensure remanent polarization.

(4) In an oriented ferroelectric thin film described in Japanese PatentLaid-open No. Hei 6-151601, an epitaxial or oriented buffer layer havinga two-layer structure on a semiconductor single crystal substrate and anepitaxial or oriented perovskite ABO₃ type ferroelectric substance isformed thereon, to obtain a highly oriented ferroelectric thin film.

In the above references, description is made of the nonvolatile memoriesusing a ferroelectric substance as a capacitor. The problems to beexamined, however, are also present in DRAMs using a ferroelectricsubstance as a capacitor.

(5) For example, as described in “Ferroelectric Thin Film IntegrationTechnology” (published by Science Forum, 1992), pages 13-16, for a 256Mb DRAM or the like, an attempt has been made to use a crystal thin filmmade from a high dielectric constant material such as BaSrTiO₃ or thelike for a capacitor.

In the above-described references (1) and (2), it is difficult tocontrol the crystal grain size and orientation of the ferroelectric thinfilm. When such a ferroelectric thin film is patterned to form a memorycapacitor, a variation in characteristics between memory cells becomeslarge because of a large variation in crystal grain size, a largervariation in crystal orientation, and a larger surface roughness of eachof the ferroelectric thin film and an electrode. This makes it difficultfor all of the memory cells to equally obtain sufficientcharacteristics, giving rise to a problem in exerting adverse effect onthe stability in manufacturing yield.

In the above-described reference (3), a variation in orientation isreduced; however, since a variation in grain size of crystal grains in amemory cell is large, a leakage current occurs, an effective voltagebetween capacitors is reduced because of concentration of an electricfield at a grain boundary portion present in the thin film in the filmthickness direction, or remanent polarization becomes uneven, whichresults in degradation of the performance of the memory cell.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-describedproblems, and to provide a ferroelectric thin film capacitor capable ofreducing a variation in characteristics between memory cells, therebyrealizing a highly integrated ferroelectric memory having an enhancedperformance at an improved manufacturing yield.

To solve the above problems, according to the present invention, thereis provided a semiconductor memory device using, as a memory capacitor,a ferroelectric thin film capacitor composed of a stacked structurehaving at least a lower electrode, a ferroelectric thin film and anupper electrode formed on a substrate, wherein a relative standarddeviation of crystal grain sizes of crystal grains of the ferroelectricthin film is controlled at a value of 13% or less; the crystal grainsare formed into columnar shapes elongated in the film thicknessdirection; and the columnar crystal grains have no grain boundary in thefilm thickness direction. With this configuration, it is possible toprevent occurrence of a leakage current and also to prevent a reductionin effective voltage applied between capacitors due to concentration ofan electric field in the ferroelectric thin film or at an interfacebetween the ferroelectric thin film and an electrode.

The lower electrode of the above capacitor may be configured as a Ptelectrode or a Pt alloy electrode, and the lower electrode may be formedsuch that the (111) faces of crystal grains are preferentially orientedin the direction perpendicular to a substrate plane. This makes itpossible to improve the orientation of a ferroelectric thin film formedon the lower electrode, and hence to further enhance the uniformitybetween memory cells. The lower electrode may be also made from acompound containing a material such as Ru, Ir, an oxide thereof or Pt,and an element contained in the ferroelectric thin film. In this case,the same effect as that described above can be achieved.

An ABO₃ type oxide having a perovskite structure may be used as theferroelectric material and the ferroelectric thin film may be formedsuch that the (111) faces of crystal grains are preferentially orientedin the direction perpendicular to the substrate plane. With thisconfiguration, it is possible to reduce the non-uniformity incharacteristics due to a variation in orientation. By use of an ABO₃type ferroelectric substance having a composition [A=Pb, B=(Zr_(1-x),Ti_(x))], there can be obtained a ferroelectric thin film having a largeremanent polarization, which film is desirable for a nonvolatile memory.Further, by use of an ABO₃ type ferroelectric substance having acomposition [A=(Ba_(1-x), Sr_(x)), B=Ti], there can be obtained aferroelectric thin film exhibiting no hysteresis at a memory servicetemperature, which film is desirable for a capacitor of a DRAM or thelike. A erroelectric thin film can be made from a material having acomposition at least part of which contains a crystalline ABO₃ typeoxide, an amorphous ABO₃ type oxide, or a mixture thereof, where A is atleast one element selected from a group consisting of Pb, La, Sr, Nd andBa; B is at least one element selected from a group consisting of Zr,Ti, Mn, Mg, Nb, Sn, Sb and In; and O is oxygen.

According to the present invention, there is provided a method ofreducing the relative standard deviation of crystal grain sizes ofcrystal grains of a ferroelectric thin film by forming micro-nucleinecessary for growth of the crystal grains on the lower electrode withless variation. The method includes the steps of forming initial nucleimade from at least one or more of metals contained in a ferroelectricthin film to be formed or an oxide or compound containing the metals, orheat-treating the lower electrode after formation thereof at a hightemperature to precipitate at least one or more of metals contained inan adhesive layer (provided between the lower electrode and a CMOSsubstrate) or an oxide or compound containing the metals on the surfaceof the lower electrode, thereby forming initial nuclei necessary forformation of micro-nuclei; and forming and crystallizing a ferroelectricthin film on the initial nuclei layer to a thickness required for asemiconductor device. With this configuration, there can be obtained aferroelectric capacitor in which the relative standard deviation of thecrystal grain sizes is small, the (111) faces of the crystal grains arepreferentially oriented in the direction perpendicular to the substrateplane, and the surface roughness is small.

Alternatively, the above initial nuclei layer to be formed on thesurface of the lower electrode may be made from an ABO₃ type oxidehaving a perovskite structure where A=Pb, B=(Zr_(1-x), Ti_(x)) orA=(Ba_(1-x), Sr_(x)), B=Ti, or made from Ti, TiO_(x), Sr or SrO_(x). Theinitial nuclei can be made from a material having a composition at leastpart of which contains a crystalline ABO₃ type oxide, an amorphous ABO₃type oxide, or a mixture thereof, where A is at least one elementselected from a group consisting of Pb, La, Sr, Nd and Ba; B is at leastone element selected from a group consisting of Zr, Ti, Mn, Mg, Nb, Sn,Sb and In; and O is oxygen. With this configuration, there can beobtained a ferroelectric thin film in which the crystal grain sizes aresmall and the relative standard deviation of the crystal grains issmall. The ferroelectric thin film thus obtained is advantageous insuppressing growth of crystal grains having the pyrochlore structure androsette-shaped ZrO_(x) crystal grains causing deterioration offerroelectric characteristics, and ensuring properties most suitable fora nonvolatile memory, that is, a large remanent polarization value, asmall leakage current, and a small film fatigue (reduction in remanentpolarization due to rewriting).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view showing the schematic configuration of a capacitorportion of a semiconductor memory device using a ferroelectric thin filmin which the relative standard deviation of crystal grain sizes is 13%or less according to one embodiment of the present invention;

FIG. 1B is a sectional view of FIG. 1A;

FIG. 2A is a top view illustrating a method of measuring crystal grainsizes of a ferroelectric thin film in an observation image (size: 1 μm×1μm) obtained by an AFM according to one embodiment of the presentinvention;

FIG. 2B is an essential portion enlarged view of FIG. 1A;

FIG. 3 is an X-ray diffraction diagram showing the result of X-raydiffraction of a ferroelectric capacitor in a semiconductor memorydevice according to one embodiment of the present invention;

FIGS. 4A and 4B are diagrams showing a correlation between an averagecrystal grain size “a” and a remanent polarization value P according toone embodiment of the present invention, and a diagram showing acorrelation between an average crystal grain size “a” and a film fatigueaccording to one embodiment of the present invention;

FIGS. 5A and 5B are diagrams showing a correlation between a relativestandard deviation σ of crystal grain sizes of a ferroelectric thin filmand a remanent polarization value P according to one embodiment of thepresent invention, and a correlation between the relative standarddeviation σ and a film fatigue according to one embodiment of thepresent invention;

FIG. 6 is a schematic sectional view illustrating a method of measuringsurface irregularities of a ferroelectric thin film by an AFM accordingto one embodiment of the present invention;

FIGS. 7A and 7B are diagrams showing a correlation between a surfaceroughness Rms and a remanent polarization value P according to oneembodiment of the present invention, and a diagram showing a correlationbetween the surface roughness Rms and a film fatigue according to oneembodiment of the present invention;

FIGS. 8A, 8B, 8C and 8D are flow charts showing a method ofmanufacturing a ferroelectric thin film according to one embodiment ofthe present invention;

FIG. 9 is a top view showing one example of a film formation apparatusfor manufacturing a ferroelectric capacitor of a semiconductor memorydevice according to one embodiment of the present invention;

FIG. 10 is a sectional view showing the schematic configuration of acapacitor portion of a semiconductor memory device using a ferroelectricthin film according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail.

(1) Semiconductor Memory Device on Which Ferroelectric Thin Film isMounted

FIG. 10 is a sectional view showing the schematic configuration of acapacitor portion of a semiconductor memory device using a ferroelectricthin film according to one embodiment of the present invention. Symbol'snumber 98 is a Si substrate. Symbol's number 101 is an underlayer LSI.Symbol's number 102 is an insulating layer. Symbol's number 81 is anadhesive layer. Symbol's number 11 is a lower electrode. Symbol's number104 is a ferroelectric layer. Symbol's number 105 is an upper electrode.Symbol's number 103 is an interconnection layer (a wiring layer).Symbol's number 106 is an interlayer insulating layer. Symbol's number107 is a protective layer. Symbol's number 108 is a sealing resin. ACMOS, which will be taken as a transistor portion of a memory cell, isformed on a Si substrate 98, and an insulating layer 102 forplanarization, insulation and protection of the CMOS. In thisembodiment, as the insulating layer 102, a SiO₂ glass film called a BPSGfilm is formed to a thickness of 300 nm. A ferroelectric capacitor isformed on the SiO₂ insulating layer 102. The ferroelectric capacitor hasa stacked structure of a Ti adhesive layer 81 (20 nm), a Pt lowerelectrode 11 (200 nm), an inventive ferroelectric substancePb_((1+y))(Zr_(1-x), Ti_(x))O₃ layer 104 (250 nm) containing crystalgrains in which a relative standard deviation of crystal grain sizes is13% or less (not more than 13%), and an upper electrode 105 (10 nm). Aninterlayer insulating layer 106 and an interconnection layer 103 forinterconnecting the capacitor electrode 105 to the transistor arestacked on the capacitor, and another interlayer insulating layer 106 isformed on the interconnection layer 103. A protective layer 107 madefrom SiO₂ or the like is formed on the interlayer insulating film 106.Finally, the entire structure is packaged by a sealing resin 108.

(2) Relative Standard Deviation of Crystal Grain Sizes of FerroelectricThin Film FIG. 1 is a view showing the schematic configuration view of acapacitor portion of a semiconductor memory device using a ferroelectricthin film 12 formed on a lower electrode 11 according to one embodimentof the present invention, wherein the ferroelectric thin film[Pb(Zr,Ti)o₃(PZT)] 12 has crystal grains 13 in which a relative standarddeviation of crystal grain sizes is 13% or less (not more than 13%). Inthe figure, FIG. 1A shows the top view, and FIG. 1B shows the sectionalview taken on a cutting plane of the top view of FIG. 1A. Here, avariation in the crystal grain sizes 14 of the crystal grains 13 isdefined as a relative standard deviation σ (unit: %) expressed byNumerical Formula 1. Depending on the large or small magnitude of therelative standard deviation σ, it can be decided whether or not thecrystal grain sizes 14 are uniform. $\begin{matrix}{\sigma = {100 \times {\left( \frac{\sqrt{\sum\limits_{i = 1}^{N}\left( {a_{i} - {a_{i}({ave})}} \right)^{2}}}{N} \right)/{a_{i}({ave})}}}} & (1)\end{matrix}$

σ: variation in crystal grain sizes (relative standard deviation)

N_(i): number of crystal grains contained in scanning line

L_(i): length of scanning line

a_(i): average crystal grain size in one scanning line

a_(i): L_(i)/N_(i)

N: number of scanning lines

a_(i)(ave): average crystal grain size in scanning lines of N pieces

a_(i) (ave): a_(i)/N

The relative standard deviation of crystal grain sizes was analyzed bytaking up a surface image or cross-sectional image of the ferroelectricthin film using a scanning electron microscope (SEM), an interatomicforce microscope (AFM) or a cross-section transmission electronmicroscope (TEM), measuring crystal grain sizes of crystal grains withina plane having the normal line in the thickness direction of theferroelectric thin film, and calculating the relative standard deviationσ of the crystal grain sizes. FIG. 2 shows a method of measuring crystalgrain sizes according to one embodiment. Straight lines (crystal grainsize calculating scanning lines 21) are set in the vertical andhorizontal directions on an observation image (size: 1 μm×1 μm) of theferroelectric thin film obtained by an AFM (atomic force microscope).Then, the number of crystal grains is counted for each scanning line.The formula for calculating the relative standard deviation of crystalgrain sizes is shown in Numerical Formula 1. By substituting the countednumber of crystal grains in Numerical Formula 1, an average crystalgrain size and a relative standard deviation are obtained. The AFM usedfor this analysis is a scanning probe microscope (trade name: Nano ScopeIII, produced by Digital Instrument Corporation in USA). The radius ofcurvature of the tip of a probe of the AFM is 10 nm and the taper angleof the tip of the probe is 35° In the case of using the probe, when agap between two adjacent ones of crystal grains on the uppermost surfaceis 80 nm, the critical penetration depth of the probe is 110 nm. In thisembodiment, the AFM measurement was performed in a tapping mode. Thedetails of the principle of the tapping mode are described in“Large-sized Sample SPM Observation System Operation Guide” (April,1996) published by Touyo Technica.

FIG. 3 shows an X-ray diffraction pattern of a PZT ferroelectric thinfilm of the present invention, wherein the abscissa designates thediffraction angle 2θ and the ordinate designates the X-ray diffractionintensity (Log I). As a measuring device, there was used a powder X-raydiffraction device using an X-ray vessel having a Cu-target as an X-raysource. In this measurement for the ferroelectric thin film, diffractionpeaks 111 and 222 were measured, and other diffraction peaks 100, 110,200, 201, 211, 202, and 301 were little measured. As a result, it wasrevealed that the ferroelectric thin film of the present invention isformed such that the (111) faces of crystal grains are preferentiallyoriented in the direction perpendicular to the substrate plane. Inaddition, diffraction peaks 111 and 222 of the Pt electrode and adiffraction peak corresponding to the Ti underlayer were observed.

FIGS. 4A and 4B show a correlation between an average crystal grain size“a” and a remanent polarization value P and a correlation between theaverage crystal grain size “a” and a film fatigue, respectively. Thefilm fatigue is defined as a percent value (unit: %) obtained bydividing a remanent polarization value after repeating writing 108 timesby the initial remanent polarization value before writing. When the filmfatigue is small, the rewritable number is large, while when the filmfatigue is large, the rewritable number is small. It should be notedthat the physical meaning and definition of each of the remanentpolarization value P and film fatigue and further a measuring/analyzingmethod thereof are described in “Ferroelectric Thin Film Memory”(published by Science Forum, 1995) and various textbooks associated withferroelectric materials. As is apparent from FIGS. 4A and 4B, for anaverage crystal grain size more than 80 nm, as the crystal grain sizebecomes smaller, the remanent polarization value P becomes larger andthe film fatigue becomes smaller (that is, the rewritable number becomeslarger), while for an average crystal grain size equal to or less than80 nm, the remanent polarization value P is kept at a specific largevalue and the film fatigue is kept at a specific small value (that is,the rewritable number is kept at a specific large value).

FIGS. 5A and 5B show a correlation between a relative standard deviationσ of crystal grain sizes and a remanent polarization value P and acorrelation between the relative standard deviation σ of crystal grainsizes and a film fatigue, respectively. In these figures, the abscissadesignates the relative standard deviation σ (unit: nm) of crystal grainsizes obtained by the above-described AFM on the basis of NumericalFormula 1. As is apparent from FIGS. 5A and 5B, for a relative standarddeviation σ of crystal grain sizes more than 13%, as the relativestandard deviation σ becomes smaller, the remanent polarization value Pbecomes larger and the film fatigue becomes smaller (that is, therewritable number becomes larger), while for a relative standarddeviation σ of crystal grain sizes equal to or less than 13%, theremanent polarization value P is kept at a specific large value and thefilm fatigue is kept at a specific small value (that is, the rewritablenumber is kept at a specific large value).

(3) Surface Roughness of Ferroelectric Thin Film

FIG. 6 is a schematic sectional view illustrating a method of measuringsurface irregularities of a ferroelectric thin film using the AFM.Symbol's number 63 is a CMOS substrate. Symbol's number 11 is a lowerelectrode. Symbol's number 13 is a crystal grain. Symbol's number 12 isa ferroelectric thin film. Symbol's number 62 is an AFM probe. An AFMprobe 62 is scanned on a ferroelectric thin film 12 while beingsubjected to vibration (tapping). At this time, on the surface of theferroelectric thin film, a recessed portion, that is, a grain boundaryportion is large vibrated, while a projecting portion, that is, acrystal grain portion is small vibrated. The amplitude of the vibrationis converted into an electric signal, and the surface irregularities aremeasured on the basis of the electric signals, to thus obtain a surfaceroughness 61.

For the surface irregular shape (profile) of the ferroelectric thin filmobtained by the AFM, SEM or TEM described in the first embodiment, thesurface roughness of the ferroelectric thin film was estimated inaccordance with the following manner.

FIGS. 7A and 7B show a correlation between a surface roughness Rms and aremanent polarization value P and a correlation between the surfaceroughness Rms and a film fatigue according to one embodiment,respectively. In these figures, the abscissa designates the surfaceroughness Rms (unit: nm) calculated from surface irregularities measuredby the AFM on the basis of Numerical Formula 2. As is apparent fromFIGS. 7A and 7B, for a surface roughness Rms more than 10 nm, as thesurface roughness Rms becomes smaller, the remanent polarization value Pbecomes larger and the film fatigue becomes smaller (that is, therewritable number becomes larger), while for a surface roughness Rmsequal to or less than 10 nm, the remanent polarization value P is keptat a specific large value. $\begin{matrix}{{R\quad m\quad s} = \left( \frac{\sqrt{\sum\limits_{i = 1}^{N}\left( {z_{i} - {z_{i}({ave})}} \right)^{2}}}{N} \right)} & (2)\end{matrix}$

Rms: surface roughness (standard deviation)

N: number of measured data

z_(i): height of measured point “i”

z_(i)(ave): average value of z_(i)

In this embodiment, the surface roughness was expressed by a standarddeviation of a difference between the maximum value and minimum value ofoverall data of surface irregularities measured by the AFM. In NumericalFormula 2, the surface roughness Rms is expressed by the standarddeviation (unit: nm). Alternatively, the surface roughness is defined asa three-dimensional average surface roughness (unit: nm) with respect toa center plane (the volume formed by the plane and the surface shapeprojecting upwardly from the plane is equal to that formed by the planeand the surface shape projecting downwardly from the plane) as shown inNumerical Formula 3. The details are described in “Large-sized SampleSPM Observation System Operation Guide” (April, 1996) published by TouyoTechnica. $\begin{matrix}{{Ra} = {\frac{1}{LxLy}{\int_{0}^{Ly}{\int_{0}^{Lx}{{f\left( {x,y} \right)}\quad {x}\quad {y}}}}}} & (3)\end{matrix}$

Ra: three-dimensional average surface roughness with respect to centerplane

Lx: dimension of surface in x-direction

Ly: dimension of surface in y-direction

f(x,y): roughness profile with respect to center plane

(4) Method of Manufacturing Ferroelectric Thin Film

FIGS. 8A to 8D shows a method of manufacturing a ferroelectric thin filmaccording to one embodiment of the present invention. To obtain aferroelectric thin film in which the relative standard deviation ofcrystal grain sizes is 13% or less, it is required to form initialnuclei necessary for growth of crystal grains. Prior to formation of aferroelectric thin film, an extremely thin layer made from at least oneor more of metals contained in a ferroelectric material or an oxide orcompound containing the metals is provided by a sputtering method orsol-gel method, followed by heat-treatment at a high temperature to forminitial nuclei 82 as shown in FIG. 8B. Alternatively, initial nuclei 82necessary for forming micro-nuclei are formed by heat-treating a lowerelectrode at a high temperature after formation of the lower electrode,to precipitate at least one or more of metals contained in an adhesivelayer 81 (disposed between the lower electrode 11 and a CMOS substrate64) or an oxide or compound containing the metals on the surface of thelower electrode 11 (see FIG. 8B). Here, the initial nuclei 82 are madefrom an ABO₃ type oxide having a perovskite structure [composition:A=Pb, B=(Zr_(1-x), Ti_(x)); or A=(Ba_(1-x), Sr_(x)), B=Ti], or made fromTi, TiO_(x), Sr, or SrO_(x). A ferroelectric thin film (a ferroelectricthin film before crystallization) 83 is then formed on the initialnuclei 82 to a thickness required for a semiconductor memory device bythe sputtering method or sol-gel method (see FIG. 8C). Then, theferroelectric thin film 83 is subjected to rapid heat-treatment by alamp using a RTA (Rapid Thermal Annealing) apparatus with the resultthat a ferroelectric thin film after crystallization 84 is formed (seeFIG. 8D). In this embodiment of the present invention, theheat-treatment is performed in a 100% N₂ atmosphere at 600° C. for 30sec. With this heat-treatment, in the ferroelectric thin film 83,crystal grains have the perovskite structure and the (111) faces ofcrystal grains are preferentially oriented in the directionperpendicular to the substrate plane. According to the above-describedmanufacturing method, it is possible to obtain a ferroelectric thin filmin which the (111) faces of crystal grains are preferentially oriented,the average crystal grain size is about 80 nm, the relative standarddeviation of crystal grain sizes is about 13%, and the standarddeviation of the surface roughness is about 10 nm. The ferroelectricthin film thus obtained is advantageous in suppressing growth of crystalgrains having the pyrochlore structure and rosette-shaped ZrO_(x)crystal grains causing deterioration of ferroelectric characteristics.As a result, a ferroelectric capacitor having a large remanentpolarization value and a small film fatigue (large rewritable number)can be obtained by use of such a ferroelectric thin film.

FIG. 9 shows a film formation apparatus for manufacturing aferroelectric thin film capacitor of a semiconductor memory device ofthe present invention. A substrate 1 carried from a substratecarrying-in chamber 99 into a substrate exchange chamber 94, and carriedamong a film formation chamber (1) 91, film formation chamber (2) 92,and film formation chamber (3) 93 in a high vacuum atmosphere via thesubstrate exchange chamber 94 by a substrate exchange arm 97. For filmformation in the film formation chamber (1) 91, a high frequencymagnetron sputter system of a multi-cathode type is adopted; and forfilm formation in each of the film formation chamber (2) 92 and filmformation chamber (3) 93, a DC magnetron sputter system of a singlecathode type is adopted. Symbol's number 95 is a gate valve. Symbol'snumber 96 is a flat cathode. Symbol's number 98 is a Si substrate. Inthis embodiment, the ferroelectric layer 83 is formed by the sputtersystem of the multi-cathode type; however, it may be formed by thesputter system of the single cathode type. In this case, a sintered bodyof a mixture of a ferroelectric PZT and a lead oxide Pbox may be used asa target. Further, the film formation may be performed by the sol-gelmethod or combination of the sol-gel method and the above-describedsputtering.

(5) IC Card on Which Semiconductor Memory Including Ferroelectric ThinFilm is Mounted

IC cards uses various kinds of semiconductor memories depending on theapplications thereof. A semiconductor memory using the ferroelectricthin film of the present invention is a nonvolatile memory. An IC cardof the present invention is advantageous in terms of limitation of chipsize, portableness, and maintenance free because any battery is notrequired to be contained for retention of data unlike a SRAM (StaticRandom Access Memory). Since the semiconductor memory including theferroelectric thin film of the present invention can be manufactured ata high yield, the IC card of the present invention can be obtained at alow cost. Also since the rewritable number of the semiconductor memoryof the present invention is made larger than that of an EEPROM(Electrically Erasable Programmable Read Only Memory) (rewritablenumber: 10⁴ to 10⁵) which is one kind of the nonvolatile memories, theservice life of the IC card of the present invention is improved, tothereby reduce the running cost. One example of a simple systemconfiguration of an IC card is described in “The whole of Non-erasableIC Memory RAM” (edited by Tomoji Kawai, published by Kougyou Chousa Kai,1996) or Text of Realize Corporation's Advanced Technical Lectureentitled “Advanced Technology of Nonvolatile Ferroelectric Thin FilmMemory and Problem Associated with Process Technology” (RealizeCorporation, 1996).

(6) Computer on Which Semiconductor Memory Including Ferroelectric ThinFilm is Mounted

A computer on which a conventional DRAM (Dynamic Random Access Memory)is mounted cannot prevent erasing of working data due to cutoff of apower supply. On the contrary, the semiconductor memory using theferroelectric thin film of the present invention is a nonvolatilememory, and accordingly, even in case of power failure, the computer ofthe present invention can retain the working state until directly beforethe power failure. The computer is not required to read the system orapplication every input of a power supply, and therefore, it can startwork directly after input of the power supply. Further, since thecomputer is not required to contain any uninterruptive power supply orbattery, it is possible to miniaturize the computer and to improveportableness of the computer due to reduction in weight or achievespace-saving thereof.

(7) Portable Information Terminal Apparatus on Which SemiconductorMemory Including Ferroelectric Thin Film is Mounted

With respect to a portable telephone representative of a portableinformation terminal apparatus of the present invention, thesemiconductor memory of the present invention contained in the portabletelephone can be driven with a small power, and is not required to beprovided with a power supply for retention of data because it is anonvolatile memory. Accordingly, as compared with a conventionalportable information terminal apparatus on which a DRAM, SRAM or EEPROMis mounted, the portable telephone of the present invention isadvantageous in reducing the weight of the main body due tominiaturization of the integrated batter and making longer the drivetime required for driving the main body without increasing the capacityof the battery.

(8) Video/Audio Apparatus on Which Semiconductor Memory IncludingFerroelectric Thin Film is Mounted

As compared with a conventional video camera containing a semiconductormemory device such as a DRAM, SRAM or EEPROM for recording video oraudio information, a video camera representative of a video/audioapparatus of the present invention is advantageous in reducing the drivepower for driving the integrated semiconductor memory device, andeliminating the necessity of provision of a power supply. This makes itpossible to reduce the weight of the main body due to miniaturization ofthe integrated battery and to make longer the drive time required fordriving the main body without increasing the capacity of the battery.

As fully described above, according to the present invention, it ispossible to realize a ferroelectric capacitor capable of reducing avariation in characteristics between memory cells, and hence to obtain ahigh quality semiconductor memory device using the ferroelectriccapacitor at a high manufacturing yield. The semiconductor memory deviceis a nonvolatile memory which makes it possible to eliminate thenecessity of provision of a power supply for retention of data, savedrive power, and improve the rewritable number. Accordingly, a system onwhich the semiconductor memory device of the present invention ismounted is capable of reducing the capacity of the inner power supply oreliminating the necessity of provision of the inner power supply,thereby realizing miniaturization of the system, increasing the servicelife thereof, and reducing the manufacturing cost thereof.

What is claimed is:
 1. A semiconductor memory device using aferroelectric thin film capacitor as a memory capacitor, said capacitorcomprising: a stacked structure having at least a lower electrode, aferroelectric thin film, and an upper electrode; wherein an averagecrystal grain size of crystal grains of said ferroelectic thin film is80 nm or more within a plane having the normal line in the thicknessdirection of said ferroelectric thin film, and a relative standarddeviation of said crystal grains is in a range of 13% or less.
 2. Asemiconductor memory device according to claim 1, wherein said crystalgrains of said ferroelectric thin film have columnar shapes elongatedsubstantially in parallel to the film thickness direction, and saidcolumnar crystal grains have no grain boundary in the film thicknessdirection.
 3. A semiconductor memory device according to claim 1,wherein a surface roughness of said ferroelectric thin film is specifiedsuch that a difference between the maximum value and the minimum valuewith respect to an average plane of surface irregularities of saidferroelectric thin film is in a range of 40% or less of an averagethickness of said ferroelectric thin film.
 4. A semiconductor memorydevice according to claim 2, wherein a surface roughness of saidferroelectric thin film is specified such that a difference between themaximum value and the minimum value with respect to an average plane ofsurface irregularities of said ferroelectric thin film is in a range of40% or less of an average thickness of said ferroelectric thin film. 5.A semiconductor memory device according to claim 1, wherein a standarddeviation of the surface roughness of said ferroelectric thin film is ina range of 10 nm or less.
 6. A semiconductor memory device according toclaim 2, wherein a standard deviation of the surface roughness of saidferroelectric thin film is in a range of 10 nm or less.
 7. Asemiconductor memory device according to claim 1, wherein saidferroelectric thin film is made from an ABO₃ type oxide having aperovskite structure, and said ferroelectric thin film is formed suchthat the (111) faces of said crystal grains are preferentially orientedin the direction perpendicular to a substrate of said semiconductormemory device.
 8. A semiconductor memory device according to claim 2,wherein said ferroelectric thin film is made from an ABO₃ type oxidehaving a perovskite structure, and said ferroelectric thin film isformed such that the (111) faces of said crystal grains arepreferentially oriented in the direction perpendicular to a substrate ofsaid semiconductor memory device.
 9. A semiconductor memory deviceaccording to claim 7, wherein said ferroelectric thin film is made froma material having a composition at least part of which contains acrystalline ABO₃ type oxide, an amorphous ABO₃ type oxide, or a mixturethereof, where A is at least one element selected from a groupconsisting of Pb, La, Sr, Nd and Ba; B is at least one element selectedfrom a group consisting of Zr, Ti, Mn, Mg, Nb, Sn, Sb and In; and O isoxygen.
 10. A semiconductor memory device according to claim 8, whereinsaid ferroelectric thin film is made from a material having acomposition at least part of which contains a crystalline ABO₃ typeoxide, an amorphous ABO₃ type oxide, or a mixture thereof, where A is atleast one element selected from a group consisting of Pb, La, Sr, Nd andBa; B is at least one element selected from a group consisting of Zr,Ti, Mn, Mg, Nb, Sn, Sb and In; and O is oxygen.
 11. An IC card on whicha semiconductor memory device described in claim 1 is mounted.
 12. An ICcard on which a semiconductor memory device described in claim 2 ismounted.
 13. An IC card on which a semiconductor memory device describedin claim 7 is mounted.
 14. A computer on which a semiconductor memorydevice described in claim 1 is mounted.
 15. A portable informationterminal apparatus on which a semiconductor memory device described inclaim 1 is mounted.
 16. A video/audio apparatus on which a semiconductormemory device described in claim 1 is mounted.
 17. A semiconductormemory device according to claim 1, wherein the Curie temperature ofsaid ferroelectric thin film is in a range of −20° C. or less, and saidferroelectric thin film does not exhibit spontaneous polarization in anenvironment upon operation of said semiconductor memory device.
 18. Asemiconductor memory device according to claim 2, wherein the Curietemperature of said ferroelectric thin film is in a range of −20° C. orless, and said ferroelectric thin film does not exhibit spontaneouspolarization in an environment upon operation of said semiconductormemory device.
 19. A semiconductor memory device according to claim 7,wherein the Curie temperature of said ferroelectric thin film is in arange of −20° C. or less, and said ferroelectric thin film does notexhibit spontaneous polarization in an environment upon operation ofsaid semiconductor memory device.